1. Field
The present invention relates to structural health monitoring (SHM) of aircraft parts. More particularly, the present invention relates to wireless, self-contained sensors communicating hierarchically with a central data acquisition module for monitoring the structural health of a composite part.
2. Related Art
Detection of structural damage or deterioration of various aircraft components is critical to insuring the safety of all occupants and cargo on board. Historically, such detection has been done manually, but this is extremely time-consuming and often ineffective because many types of damage and/or deterioration is difficult to detect with the naked eye.
Automated, non-manual technologies for aircraft structural health monitoring (SHM) are often more efficient and effective than manual detection methods, but are presently in early stages of development. One known type of SHM system includes several independent piezoelectric sensors, glued or otherwise affixed to an aircraft structure such as a wing, and wired to a data acquisition box on-board the aircraft or connected through an electrical bus. These sensors may produce an electric signal in response to various stimuli, such as vibration, and the data acquisition box may store these signals for later processing or may process these signals itself to determine the structural health of an area of the aircraft structure adjacent to the sensor. However, because the sensors and wires are glued to the exterior of the aircraft structure, they are susceptible to damage.
For composite aircraft, these problems can be largely avoided by embedding the SHM hardware within the composite. However, studies have shown that sensors embedded within a composite laminate can cause resin buildup in the vicinity of the sensor, which can initiate cracking in the composite part. Studies have also shown that this predisposition to crack initiation can be minimized by punching out a pocket in the ply stack-up for the sensor. However, such pockets are difficult to manufacture and can decrease the stress allowed for a given composite part due to the cuts made in the fiber in the local area of each sensor.
Embedding the sensors in a composite part and connecting the grid of sensors together or to a central bus can also slow down the manufacturing process. For example, in an automated process such as fiber tow placement or filament winding, the fiber placement process would have to be halted several times to place sensors, make the appropriate connections, and verify that all connections were secure before continuing with the fiber placement. There also exists a risk that the subsequent tows would dislodge sensors or wires. Then, if a sensor is faulty, there is no simple way to remove and replace the embedded sensor without affecting the structural integrity of the composite part.
Additionally, routing and gluing wires and connectors around complex structures and systems can also be problematic. To solve this particular problem, another type of SHM system uses wireless sensors to communicate with the data acquisition box. However, some sensors are physically located at farther distances from the data acquisition box than others. Therefore, some sensors must send the wireless signal farther, causing those sensors to consume a greater amount of power. This need for power limits how small the batteries for such wireless sensors may be. Additionally, the farther that each wireless sensor must send a signal, the more likely it is that the signal may experience some type of interference.
Accordingly, there is a need for an improved method of monitoring the structural health of an aircraft part that does not suffer from the problems and limitations of the prior art.